Technetium-99m (“Tc-99m”) is the most commonly used radioisotope in nuclear medicine. Tc-99m is used in approximately two-thirds of all imaging procedures performed in the United States. Tens of millions of diagnostic procedures using Tc-99m are undertaken annually. Tc-99m is a daughter isotope produced from the radioactive decay of molybdenum-99 (“Mo-99”). Mo-99 decays to Tc-99m with a half life of 66 hours.
The vast majority of Mo-99 used in nuclear medicine in the U.S. is produced in aging foreign reactors. Many of these reactors still use solid highly enriched uranium (“HEU”) targets to produce the Mo-99. HEU has a concentration of uranium-235 (“U-235”) of greater than 20%. Maintenance and repair shutdowns of these reactors have disrupted the supply of Mo-99 to the U.S. and to most of the rest of the world. The relatively short half-life of the parent radioisotope Mo-99 prohibits the build-up of reserves. One of the major producers, The National Research Reactor in Canada, will cease production in 2016.
An alternative strategy for providing Mo-99 is based upon the use of low enriched uranium (LEU), which presents a much lower nuclear proliferation risk than HEU. LEU has a concentration of U-235 of less than 20%, and many international Mo-99 producers are converting from HEU to LEU solid targets for Mo-99 production.
Several of the technologies currently being considered for the domestic supply of Mo-99 are based on the fission of U-235 in mildly acidic solutions of LEU, including the Aqueous Homogenous Reactor concept and an Accelerator-based concept which provides an external source of neutrons. Only a small fraction of the U-235 present in the acidic solution will undergo fission, as is also the case with solid target irradiation. Fission of U-235 generates a variety of fission products, one of which is Mo-99. The uranium in the mildly acidic solution is in the +VI oxidation state and in the chemical form of the uranyl di-oxo di-cation (UO22+).
Some form of enriched uranium (HEU and/or LEU) is used for the production of Mo-99. After the fission process, the remaining uranium is typically discarded along with other fission products as waste. Recycling the uranium for additional production of Mo-99 would minimize the waste while maximizing the utilization of the uranium.
Therefore, an object of the present invention is to provide a process for recycling uranium after it has been used for the production of Mo-99.
Another object is to provide a process for producing Mo-99 using recycled uranium.